In recent years, soft silicone hydrogel contact lenses are increasingly becoming popular because of their high oxygen permeability and comfort. However, a silicone hydrogel material typically has a surface or at least some areas of its surface which is hydrophobic (non-wettable). Hydrophobic surface or surface areas will up take lipids or proteins from the ocular environment and may adhere to the eye. Thus, a silicone hydrogel contact lens will generally require a surface modification.
A known approach for modifying the hydrophilicity of a relatively hydrophobic contact lens material is through the use of a plasma treatment, for example, commercial lenses such as Focus NIGHT & DAY™ and O2OPTIX™ (CIBA VISION), and PUREVISION™ (Bausch & Lomb). Advantages of a plasma coating is its durability, relatively high hydrophilicity (or good wettability), and low susceptibility to lipid and protein deposition and adsorption. But, plasma treatment of silicone hydrogel contact lenses may not be cost effective, because the preformed contact lenses must be dried before plasma treatment and because of relative high capital investment associated with plasma treatment equipments.
Another approach for modifying the surface hydrophilicity of a silicone hydrogel contact lens is the incorporation of wetting agents (hydrophilic polymers) into a lens formulation for making the silicone hydrogel contact lens as proposed in U.S. Pat. Nos. 6,367,929, 6,822,016, 7,052,131, and 7,249,848. This method may not require additional posterior processes for modifying the surface hydrophilicity of the lens after cast-molding of silicone hydrogel contact lenses. However, wetting agents may not be compatible with the silicone components in the lens formulation and the incompatibility may impart haziness to the resultant lenses. Further, such surface treatment may be susceptible to lipid deposition and adsorption. In addition, such surface treatment may not provide a durable surface for extended wear purpose.
A further approach for modifying the hydrophilicity of a relatively hydrophobic contact lens material is a layer-by-layer (LbL) polyionic material deposition technique (see for example, U.S. Pat. Nos. 6,451,871, 6,717,929, 6,793,973, 6,884,457, 6,896,926, 6,926,965, 6,940,580, and 7,297,725, and U.S. Patent Application Publication Nos. US 200710229758A1, US 200810174035A1, and US 2008/0152800A1). This technique can provide a cost effective process for rendering a silicone hydrogel material wettable. However, such LbL coating may not be suitable for extended wear purpose, because it may be less durable than a plasma coating and may not be compatible with the preservatives in some lens care solutions in the market.
A still further approach for modifying the hydrophilicity of a relatively hydrophobic contact lens material is to attach hydrophilic polymers onto contact lenses according to various mechanism (see for example, U.S. Pat. No. 6,099,122, U.S. Pat. No. 6,436,481, U.S. Pat. No. 6,440,571, U.S. Pat. No. 6,447,920, U.S. Pat. No. 6,465,056, U.S. Pat. No. 6,521,352, U.S. Pat. No. 6,586,038, U.S. Pat. No. 6,623,747, U.S. Pat. No. 6,730,366, U.S. Pat. No. 6,734,321, U.S. Pat. No. 6,835,410, U.S. Pat. No. 6,878,399, and U.S. Pat. No. 6,923,978). For example, U.S. Pat. No. 6,436,481 discloses the use of plasma-induced graft polymerization to form a primary coating with reactive groups including azlactone, amine, hydroxyl, carboxylic. A secondary coating, composed of hydrophilic polymers or materials, is attached to the primary coating to enhance surface hydrophilicity and wettability. Although those techniques can be use in rendering a silicone hydrogel material wettable, they may not be cost-effective and/or time-efficient for implementation in a mass production environment, because they typically require relatively long time and/or involve laborious, multiple steps to obtain a polymeric hydrophilic coating.
In another example, U.S. Pat. No. 6,440,571 discloses a method for modifying the surface of a medical device (including a contact lens) to increase its biocompability or hydrophilicity by coating the device with a hydrophilic polymer by means of reaction between reactive functionalities on the hydrophilic polymer which functionalities are complementary to reactive functionalities on or near surface of the medical device. U.S. Pat. No. 6,440,571 discloses that the functionalities on or near the surface of the contact lens can be azlactone groups which are introduced by copolymerizing a lens formulation including an azlactone-containing vinylic monomer, even though no actual example is provided. However, it fails to disclose and recognize that the amount of azlactone-containing vinylic monomer present in the lens formulation and subsequently in the resultant lenses has dual effects on the resultant lenses, the extent of swelling of the contact lenses upon the ring-opening hydrolysis of the azlactone groups and the efficiency in covalently attaching a hydrophilic polymer coating. The higher the amount of azlactone-containing vinylic monomer present in the lens formulation, the larger the lens swelling and the more wettable the surface of the lens (due to the high efficiency of the covalent attachment of a coating of hydrophilic polymer onto the lens surface). In contrast, the lower the amount of azlactone-containing vinylic monomer present in the lens formulation, the smaller the lens swelling and the less wettable of the surface of the lens (due to the low efficiency of the covalent attachment of a coating of hydrophilic polymer onto the lens surface). As such, the method disclosed in U.S. Pat. No. 6,440,571 may not be useful for modifying the surface wettability of silicone hydrogel contact lenses because it cannot provide a silicone hydrogel with a wettable surface while not causing the lens swelling significantly.
In view of above, there is a need for a method of producing silicone hydrogel contact lenses with wettable and durable coating (surface) in a cost-effective and time-efficient manner.